The present invention relates to combustion systems and, more particularly, relates to devices for inhibiting formation of oxides of nitrogen (NO.sub.x) by combustion systems.
As a result of the combustion process, combustion systems normally generate gaseous combustion products which include oxides of nitrogen (NO.sub.x) which are vented to atmosphere as flue gas. It is desirable to limit these NO.sub.x emissions since NO.sub.x is considered a pollutant and combustion systems sold in certain jurisdictions must meet strict NO.sub.x emmission standards.
A novel technique for limiting NO.sub.x emissions from a combustion system is disclosed in copending U.S. patent application Ser. No. 509,504 filed June 30, 1983 abandoned, filed as continuation in Ser. No. 761,336 entitled "A Device For Inhibiting NO.sub.x Formation by a Combustion System" with Chester D. Ripka, et al. as inventors. According to this novel technique, NO.sub.x emissions from a combustion system are limited by providing the combustion system with a special device at each burner location to inhibit formation of NO.sub.x by the combustion system. The special device is a piece of material which is sized, configured, and positioned relative to the combustion flame produced by the burner to temper the combustion flame by absorbing thermal energy from the combustion flame. The device is designed to absorb thermal energy from the combustion flame at a rate which limits peak flame temperatures and residence times at these peak flame temperatures to levels which inhibit formation of NO.sub.x, while allowing substantially complete combustion of fuel supplied to the burner.
A device of the type described above may be used to limit NO.sub.x emissions from a combustion system such as a gas-fired furnace having monoport inshot burners which each burn fuel to form a combustion flame which is projected through an inlet opening into a heat exchanger for the combustion system. However, if the furnace is frequently cycled on and off, then the device must be able to withstand frequent thermal cycling from room temperatures to combustion temperatures without breaking, bending, cracking or otherwise mechanically failing. Also, to ensure that the combustion process of the furnace is not adversely affected by the presence of the device, the device should not adversely interfere with the flow of products of combustion away from the combustion zone for each burner. Further, the device should be relatively easy and inexpensive to manufacture and easy to install, so that the device is practical from a cost-effectiveness viewpoint and so that the device is suitable for retrofitting furnaces having such monoport inshot burners.